Gas spring with means for impeding piston movement away from one terminal position

ABSTRACT

A gas spring of the piston-and-cylinder type in which the two compartments of the cylinder cavity, separated by a piston assembly, are connected by a first passage. A valve arrangement on the piston assembly defines a second passage between the compartments and closes in response to movement of the piston assembly away from a terminal position in the cylinder while opening in response to movement of the piston assembly towards the terminal position. Releasable locking structure carried in part by the cylinder and in part by the piston assembly cooperates to close the first passage when the piston assembly approaches the terminal position, thereby to hold the piston assembly in such terminal position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of our copending U.S.application Ser. No. 938,228, filed Aug. 30, 1978, and now abandonedwhich is a division of U.S. application Ser. No. 791,011, filed Apr. 26,1977, now U.S. Pat. No. 4,166,612 and repeats those portions of thedisclosure and claims of the parent applications that relate to thedivisional subject matter. The remaining portions of those applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to gas springs and like devices andparticularly to improved devices of the piston-and-cylinder type inwhich the piston rod may be locked automatically at one end of itsstroke against a force tending to expel the piston rod.

2. The Prior Art

Gas springs, which are devices of the type described, are employedbetween the body of a motor car or like vehicle and a cover, such as ahood, trunk lid, or door mounted on the body for movement about ahorizontal axis. The fluid pressure in the spring tends to move thepiston in a direction to expel the piston rod from the cylinder cavityand thereby to move the cover in an upward direction, whereby little orno manual effort is needed for lifting the cover. For downward movementof the cover, only the difference between the forces exerted on thecover by gravity and by the gas in the spring need to be overcome byhand. It is known to equip such gas springs with devices which impedemovement of the piston rod from one of its axially terminal positionsand thereby hold the cover in a lowermost angular position against theforce of the gas in the spring independently of a latch or lock securingthe cover directly to the vehicle body. In our earlier applications Ser.No. 938,228 now abandoned and Ser. No. 791,011, now U.S. Pat. No.4,166,612 we have disclosed gas springs equipped with improved devicesfor accomplishing this function in a new and advantageous manner.

The present application is directed to the subject matter of our priorapplication Ser. No. 938,228 and to still further improvements thereinhaving utility in gas springs and other devices of thepiston-and-cylinder type referred to.

SUMMARY

In accordance with the invention, a piston-and-cylinder device includesa cylinder defining a sealed cavity therein and a piston assembly,including a piston and piston rod, partly received in the cavity andaxially movable towards and away from a terminal position. The pistonassembly is formed with a normally-open first passage which extendsaxially across the piston and connects the compartments of the cylindercavity separated by the piston. The piston rod is fastened to the pistonfor joint movement and extends from the piston through one of thecompartments and axially outward of the cylinder cavity. A valvearrangement defines a second passage extending between the compartmentsand responds to movement of the piston assembly away from the terminalposition to close the second passage, while opening the same in responseto assembly movement towards the terminal position. Locking structurecarried in part by the cylinder and in part by the piston assemblycloses off the first passage when the piston assembly approaches itsterminal position, thereby permitting the piston assembly to be retainedat the terminal position due to the action of the aforementioned valvearrangement in closing the second passage.

In one embodiment, the locking structure includes an open-ended plug onthe cylinder which receives an extension on the piston assembly, whenthe piston assembly approaches and is at the terminal position, to closeoff the first passage between the cavity compartments. In a secondembodiment, the piston assembly itself is open-ended, and the extensionreceived therein at the terminal position of the piston assembly is inthis instance carried by the cylinder. If desired, a third passageacross the piston may be provided, with additional valve means beingprovided to open such passage upon the application to the piston rod ofa predetermined force directed away from the terminal position of thepiston assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, additional objects and the attendant advantages of theinvention will readily be appreciated as the same become betterunderstood from the following detailed description of preferredembodiments when considered in connection with the appended drawings, inwhich:

FIG. 1 shows a gas spring of the invention in elevational section on itsaxis; and

FIGS. 2, 3 and 4 illustrate modifications of the spring of FIG. 1 incorresponding views.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Except for the reference numerals which have been changed in part hereinfor clarity of description, FIG. 1 corresponds to FIG. 6 of applicants'parent U.S. application Ser. No. 938,228 now abandoned and U.S. Pat. No.4,166,612. The spring illustrated in FIG. 1 is of conventional externalappearance. It has a cylinder 1 and a coaxial piston rod 2 extendingaxially outward of the cylinder through an annular, radial end wall 6 ofthe cylinder. An annular gasket 7 carried by the end wall 6 seals thecylinder cavity from the atmosphere, the other end wall of the cylinderbeing imperforate. The spring may be mounted between a vehicle body anda cover by means of fastening lugs 8A and 8B on the piston rod 2 andcylinder wall 9, respectively. As shown in FIG. 1, the gas spring is ator near its minimum overall length, and the piston rod 2 is at or nearits innermost axial position within the cylinder 1, the inward stroke ofthe piston rod 2 being determined in part by the vehicle elementsattached to the fastening lugs 8A and 8B.

A piston assembly 3, of which the piston rod 2 is a part, axiallydivides the cavity of the cylinder 1 into compartments 4, 5,respectively remote from and adjacent to the end wall 9. The pistonassembly 3 is of the type disclosed in Schnitzius U.S. Pat. No.3,919,509, the pertinent portions of which are hereby incorporated intothis application, to provide controlled communication between thecompartments 4, 5 through a restricted passage. Air or nitrogen atsuperatmospheric pressure is confined in the cylinder cavity and tendsto expel the piston rod 2 at a velocity controlled by the rate of gasflow from the compartment 4 into the compartment 5. The structuredescribed so far and its operation are too well known to require moredetailed description.

The lower end wall 9 of the cylinder 1 is formed by a cup-shaped brakeblock or plug 10 which defines interiorly thereof a recess 11 that openstoward the compartment 5 in the illustrated intermediate position of thepiston assembly 3. The piston assembly 3 includes a mounting tube 12coaxially attached, e.g., by welding, to the inner end of the piston rod2. An annular piston disk 13 and a tubular element 14 are coaxiallysecured on the tube 12 between a radial face of the disk 13 and a flange15 of the tube 12. The external diameter of the element 14 is greaterthan the diameter of the piston rod 2. The flange 15 bounds an axiallyopen orifice of the bore 16 in the tube 12 which, jointly with a short,coaxial bore 17 in the piston rod 2 and a radial throttling bore 18 inthe piston rod, provides a first passage connecting the compartments 4,5 in the illustrated position of the piston assembly.

The piston assembly 3 further includes a spider-mounted ring 19 fixedlysecured between the piston rod 2 and a collar of the disk 13. The outerdiameters of the disk 13 and the ring 19 are smaller than the innerdiameter of the cylinder 1. A piston ring 20 is axially confined betweenthe disk 13 and the ring 19 in frictional engagement with the cylinder 1for limited movement between the illustrated position of abuttingengagement with the ring 19, in which it seals the annular gap betweenthe disk 13 and the cylinder 1, and a position of abutting engagementwith the ring 19, in which the piston ring 20 opens a second passageconnecting the compartments 4, 5. A sealing ring 22 projects radiallyfrom the tubular element 14 between the disk 13 and the flange 15.Hydraulic brake fluid 24 fills the lower portion of the compartment 5and the interior space 11 in the plug 10. As already noted, the sealedcylinder cavity is otherwise filled with air or nitrogen under apressure much higher than atmospheric pressure.

Fluid pressure in the connected compartments 4, 5 tends to expel thepiston rod 2 from the cylinder 1. During the outward movement of thepiston rod 2, friction engagement of the piston ring 20 with thecylinder 1 holds the piston ring against the disk 13. Outward piston rodmovement is impeded by the throttling effect of the bore 18 on fluidflow between the compartments.

When the piston rod 2 is moved inward of the cylinder 1 by externalforces, the ring 20 lags behind the disk 13 and a passage of relativelylow flow resistance is opened through the gap between the disk 13 andthe cylinder 1. Fluid may simultaneously flow between the compartments4, 5 through the bores 16, 17 and 18. After the element 14 enters thespace 11 in the plug 10, the sealing ring 22 is radially compressed andcloses the passage between the compartment 5 and the space 11, whichcommunicates with the compartment 4. As will be appreciated, this alsocloses off communication between the compartments 4 and 5 via thepassage 16, 17, 18. Thereafter, fluid can be displaced from the space 11only through the throttling bore 18, and there is a sudden, thoughsmall, increase in the resistance of the piston rod to inward movement.If the external force on the piston rod 2 is relaxed, the fluid pressurein the space 11 starts pushing the piston assembly 3 upward until thepiston ring 20 engages the disk 13 and thereby seals the passage betweenthe compartments 4 and 5 through the gap around the disk 13. The pistonassembly 3 is thereby locked in its terminal position near the plug 10in which the axial forces exerted by fluids in the compartments 4, 5 andthe space 11 balance each other. The locking force, however, may bereadily overcome by an outwardly directed force exerted on the pistonrod 2 in the manner described in the referenced portions of parentapplication Ser. No. 938,228.

Except as otherwise noted the embodiment of FIG. 2 is the same as theembodiment of FIG. 1, and it will be understood that like referencenumerals refer to like parts. As depicted in FIG. 2, the disk 13 hasformed therein a plurality of circumferentially spaced, axiallyextending bores 25 (only one of which is shown) which communicate withthe compartment 4 through the openings in the spider-mounted ring 19 andthe central opening in the piston ring 20. The bores 25 are normallyclosed on the lower side thereof by a valve ring 26, which, asillustrated in FIG. 2, is biased towards the closed position by ahelical compression spring 27 captured on the tubular element 14 by aspring clip 28. The operation of the embodiment of FIG. 2 is similar tothat of FIG. 1. Thus the piston assembly 3 will be automatically lockedat the inner terminal position in the manner described above inconnection with FIG. 1.

Upon the application of an external force pulling the piston rod 2outward of the cylinder 1, the resulting expansion of the compartment 5and contraction of the compartment 4 causes a pressure differentialbetween the two compartments which ultimately causes the valve ring 26to open the bores 25 against the restraint of the spring 27, and theensuing flow of fluid inward of the compartment 5 facilitates furtherwithdrawal of the piston rod 2 until the sealing ring 22 is disengagedfrom the plug 10 and an additional passage between the compartments 4, 5is opened via the bores 16, 17 and 18. As will be appreciated, thelocking force of the device may be tailored to the requirements ofspecific applications by a spring 27 of appropriate strength.

The gas springs illustrated in FIGS. 3 and 4 are likewise basically thesame in overall appearance and structure as the embodiment of FIG. 1,and, here again, like reference numerals as used to identify like parts.In these embodiments, however, the inner end of each cylinder rod 2 istubular and externally threaded at 30 for engagement with an internallythreaded annular piston disk 13. Also, the devices of FIGS. 3 and 4 arespecially adapted for use with only a single operating fluid, eithergaseous or liquid. No fluid interface is illustrated, therefore, inFIGS. 3 and 4. As in the prior embodiments, the disk 13 is smaller indiameter than the inner wall of the cylinder 1. An apertured,spider-mounted ring 19, also of smaller diameter than the cylinder wall,is captured between a shoulder on the disk 13 and a spring clip 32 onthe piston rod 2. As will be understood, the ring 19 limits axialshifting of the piston ring 20 in an upward direction away from the disk13. The compartments 4, 5 on axially opposite sides of the disk 13 areconnected in the illustrated position of the piston assembly 3 by afirst passage through a wide axial bore 16 and a relatively wide radialbore 18 in the piston rod 2. A second passage connecting thecompartments 4, 5 via the gap around the disk 13 is opened by the pistonring 20 acting as a valve when the piston assembly moves inward of thecylinder 1.

As illustrated in FIGS. 3 and 4, the end wall 9 includes a cylindricalprojection 34 that extends into the compartment 5 in coaxial alignmentwith the large bore 16 in the piston rod 2, and in both embodimentscarries a sealing ring 36 adjacent its free end. When the pistonassembly 3 is moved downward from the position illustrated in FIGS. 3and 4 against the restraint of a compressed fluid filling the cylindercavity, the rod 34 enters the bore 16 and the sealing ring 36 closes thepassage 16, 18 between the compartments 4, 5 through the piston rod 2.Fluid trapped below the piston disk 13, however, can continue to flow tothe compartment 4 through the annular gap between the disk 13 and theinner cylinder wall, which is opened by the piston ring 20 duringmovement of the piston rod 2 inward of the cylinder cavity. When theinward force applied to the piston rod 2 is relaxed, the disk 13 ismoved slightly upward into sealing engagement with the stationary pistonring 20, and the piston assembly 3 is thus locked near its lowermostposition in pressure equilibrium between the bodies of fluid in thecompartments 4, 5.

The embodiment of FIG. 4 differs from that of FIG. 3 in that theprojection 34 on the end wall 9 is formed with an upwardly open, axialbore 38 and a radial bore 40 which connects the lower end of the axialbore 38 to the compartment 5. An annular rubber seal member 42 normallycloses the orifice of the radial bore 40 in the cylindrical face of theprojection 34.

When the piston rod 2 is pushed inward of the cylinder 1, the rod 34enters the bore 16 in the piston rod 2 as described with reference toFIG. 3 to close the passage between the compartments 4, 5 through thepiston rod 2. If the piston rod 2 thereafter is pulled outward of thecylinder 1, a pressure differential between the compartments 4, 5 causesthe rubber seal member 42 to be pushed away from the orifice of theradial bore 40, thereby opening a by-pass which facilitatesdisengagement of the rod 34 from the piston rod 2 until the sealing ring36 is disengaged from the wall of the bore 16. As will be appreciated,therefore, the embodiment of FIG. 3 operates in basically the samemanner as the embodiment of FIG. 1, while the embodiment of FIG. 4operates like that of FIG. 2.

The terms "upper" and "lower" and analogous terms have been used withreference to the drawing for convenient description of what isillustrated. If a cylinder 1 is partly filled with liquid and partlywith gas, it is preferred that the terminal, locked position be reachedwhen the piston assembly 3 is in or contiguously adjacent its lowestposition relative to the cylinder. When only one fluid, gaseous orliquid, is employed, as shown for example in FIGS. 3 and 4, gravity hasno effect on operation, and the piston-and-cylinder device may bemounted in any desired orientation in space.

The projections 34 in the embodiments of FIGS. 3 and 4 make itimpractical for the piston rod to extend from the disk 13 outward of thecylinder cavity through the compartment 5. In the device of FIGS. 2 and3, however, the piston rod 2 may if desired be attached to the flangedend of the tubular element 12 without blocking the orifice of the bore16 and extend outward of the cylinder cavity through a gasketed openingin the end plug 10 while the annular end wall 6 is sealed and carriesthe mounting lug 8B. The bore 16 would then communicate directly withthe compartment 4, and in such case its orifice may be reduced in sizeto duplicate the afore-described throttling effect of the radial bore18.

Other variations of the illustrated embodiments of the invention willreadily suggest themselves on the basis of the above teachings. Forexample, if a spring action is not needed but the locking function is tobe maintained, another rod, equal in cross section to the piston rod 2,may be mounted coaxially on the tubular element 12 in the embodiments ofFIGS. 1 and 2 for movement through an aperture in the plug 10 and asuitable gasket without blocking the orifice of the bore 16. In thiscase, the plug 10 could be moved to another suitable location within thecylinder 1. In this modified piston-and-cylinder device, liquid maycompletely replace the compressed nitrogen in the cylinder 1. It shouldbe understood, therefore, that the foregoing disclosure relates only topresently preferred embodiments, and that it is intended to cover allchanges and modifications of the examples of the invention herein chosenfor the purpose of the disclosure which do not constitute departuresfrom the spirit and scope of the invention set forth in the appendedclaims.

What is claimed is:
 1. A cylinder-and-piston device, comprising:(a) acylinder having an axis and defining a sealed cavity therein; (b) apiston assembly axially movable in said cavity towards and away from aterminal position, and including:(1) a piston axially dividing saidcavity into first and second compartments; (2) means defining a firstpassage extending axially across said piston for connecting saidcompartments when said assembly is remote from said terminal position;(3) a piston rod fastened to said piston for joint movement therewithand extending from the piston through said first compartment and axiallyoutward of said cavity; (4) means defining a second passage extendingaxially across said piston for connecting said compartments; and (5)valve means for closing said second passage, said valve means operatingto close said second passage only in response to movement of said pistonassembly away from said terminal position, said valve means opening saidsecond passage in response to movement of said piston assembly towardssaid terminal position; and (c) locking means carried in part by saidcylinder in said cavity and in part by said piston assembly for closingsaid first passage when said piston assembly approaches said terminalposition so that once said piston assembly is adjacent said terminalposition, movement of said piston assembly away from said terminalposition closes said second passage, thereby preventing fluidcommunication between said first and second compartments and therebyretaining said piston assembly adjacent said terminal position.
 2. Adevice as set forth in claim 1, further comprising a fluid undersuperatmospheric pressure in at least one of said compartments.
 3. Adevice, as set forth in claim 2, wherein said locking means is operativeto maintain said first passage closed while said piston assembly isadjacent said position and to permit fluid flow through said firstpassage when said piston assembly is remote from said position.
 4. Adevice as set forth in claim 1, wherein said locking means includes atubular extension on said piston assembly projecting from said pistoninto said second compartment, said tubular portion being formed with anorifice of said first passage, said locking means sealing said orificefrom said second compartment when said piston assembly is adjacent saidposition.
 5. A device as set forth in claim 4, wherein said lockingmeans defines a chamber communicating with said second compartment whensaid piston assembly is remote from said position and communicating withsaid orifice in all positions of said piston assembly, said lockingmeans sealing said chamber from said second compartment when said pistonassembly is in said position thereof.
 6. A device as set forth in claim1, wherein said first passage has an axially open orifice in said pistonassembly, and said locking means sealingly engages said orifice whensaid piston assembly approaches said position.
 7. A device as set forthin claim 6, wherein said locking means includes a locking memberdimensioned for axial movement inward of said passage through saidorifice.
 8. A device as set forth in claim 1, wherein said locking meansincludes pressure relief valve means responsive to a sufficient forceapplied axially to said piston assembly for moving the assembly in adirection away from said position for opening a third passage connectingsaid compartments while said first and second passages are closed.
 9. Adevice as set forth in claim 8, wherein said piston assembly is formedwith said third passage.
 10. A device as set forth in claim 1, whereinsaid terminal position is that position in which said first compartmenthas its greatest volume and said second compartment has its smallestvolume.
 11. A cylinder-and-piston device, comprising:(a) a cylinderhaving an axis and defining a sealed cavity therein; (b) a pistonassembly axially movable in said cavity between two axially terminalpositions, said assembly including(1) piston means axially dividing saidcavity into two compartments, and (2) a piston rod fastened to saidpiston means for joint movement, said piston rod extending axially fromsaid piston through one of said compartments and outward of said cavity;(c) locking means for impeding axial movement of said piston away fromone of said terminal positions thereof, said locking means including:(1)a plunger member fastened to said piston for joint movement and axiallyprojecting from said piston into the other compartment, (2) a lockingmember axially secured to said cylinder in said other compartment andformed with an axially open recess receiving said locking member in saidone terminal position of said piston, and (3) cooperating engagementmeans on said members impeding relative axial movement of said memberswhen said plunger member is received in said recess; and (d) fluid insaid compartments,(1) said piston assembly and said plunger being formedwith respective portions of a first passage having respective orificesin said one compartment and in said recess when plunger member isreceived in said recess, (2) said piston bounding a second passageconnecting said compartments, (3) said locking means further includingvalve means closing said second passage in response to incipientmovement of said piston away from said one terminal position thereof,(4) said first passage constituting the sole connection between saidother compartment and said one compartment when said valve means closessaid second passage and said plunger member is received in said recess.12. A device as set forth in claim 11, wherein said engagement meansincludes a resiliently compressible sealing element on one of saidmembers sealing said recess from a portion of said other compartmentadjacent said piston in said one terminal position of said piston.
 13. Adevice as set forth in claim 12, wherein said second passage extendsradially between said piston and said cylinder, and said valve meansincludes a valve member mounted on said piston for axial movementbetween a passage-closing and a passage-opening position, said valvemember slidably engaging said cylinder.
 14. A device as set forth inclaim 13, wherein said first passage is permanently open and includes aportion of restricted flow section.
 15. A device as set forth in claim14, wherein said piston has respective, annular face portions in saidcompartments about said piston rod and about said plunger member,respectively, the area of the face portion in said one compartment beinggreater than the area of the face portion in said other compartment. 16.A device as set forth in claim 11, wherein said fluid includes an amountof liquid sufficient to fill said first passage and said othercompartment when said plunger member is received in said recess.
 17. Adevice as set forth in claim 11, wherein said one terminal position isthat in which said one compartment has its greatest volume and saidother compartment has its smallest volume.
 18. A cylinder-and-pistondevice adapted so as to be mounted between a mass and a movable objectattached to said mass for movement between a lower terminal position andan upper terminal position, said cylinder-and-piston device tending tobias said movable object toward said upper terminal position, andtending to retain said movable object adjacent said lower terminalposition in the absence of an external force, the improvement whereinsaid cylinder-and-piston device comprises:(a) a cylinder having an axisand defining a sealed cavity therein; (b) a piston assembly axiallymovable in said cavity toward and away from a terminal positioncorresponding to said lower terminal position of said movable object,and including:(1) a piston axially dividing said cavity into first andsecond compartments; (2) means defining a first passage extendingaxially across said piston for connecting said compartments when saidassembly is remote from said terminal position; (3) a piston rodfastened to said piston for joint movement therewith and extending fromthe piston through said first compartment and axially outward of saidcavity; (4) means defining a second passage extending axially acrosssaid piston for connecting said compartments; and (5) valve means forclosing said second passage, said valve means operating to close saidsecond passage only in response to movement away from said terminalposition, said valve means opening said second passage in response tomovement of said piston assembly towards said terminal position; and (c)locking means carried in part by said cylinder in said cavity and inpart by said piston assembly for closing said first passage when saidpiston assembly approaches said terminal position so that once saidpiston assembly is adjacent said terminal position, movement of saidpiston assembly away from said terminal position closes said secondpassage to prevent fluid communication between said first and secondcompartments, thereby retaining said piston assembly adjacent saidterminal position and said movable object adjacent said lower terminalposition.